This application is based upon and claims priority to German Patent Application 199 27 933.0 filed Jun. 18, 1999, which application is herein expressly incorporated by reference.
The invention relates to a sieve for a thresher, especially to a combine-harvester which harvests grains. Its sieve surface has, when viewed in a section arranged parallel to the conveying direction, a base-profile with a zigzag arrangement.
In combine-harvesters, as a rule, two superimposed supported sieves are positioned and connected downstream from the threshing device. The sieves are subjected to a shaking motion which, in turn, transports the to be cleaned harvested material in the conveying direction. The upper sieve serves to separate coarser chaff and straw parts, in the technical jargon also called non-grain components, from the grains. The upper sieve transports these to the back out of the cleaning system. The sieved harvesting material falls through the upper sieve onto the fine sieve arranged below it. The rest of the non-grain-components of the harvesting material is separated by means of this sieve and is also transported to the back. Both sieves are blown through by an air stream of a fan. The air stream lifts the lighter chaff and straw parts up, so that these are also transported by means of the air stream over the sieves to the back. The specifically heavier grains fall through the sieves and are conveyed in the known way by the conveying equipment to a grain tank or are filled into sacks. Ears or panicle parts, which may still contain grains, fall through a sieve extension of the upper sieve or reach via the lower sieve a conveyor. The conveyor conveys these parts again to the threshing device for renewed threshing. Modern combine-harvesters in order to increase efficiency, have very aggressive threshing mechanisms, for example multipath drum systems or friction cylinder systems.
A combine-harvester with sieve devices is disclosed in U.S. Pat. No. 5,176,574. A disadvantage of this system is that along with the grain and chaff, a large amount of threshed straw is conveyed onto the cleaning sieves. This has the effect that, when the threshing devices are getting more powerful, the load of the downstream connected sieves is disproportionally increased. For example, the power increase is reversed to the opposite by the aggressive threshing devices when dry and brittle straw is threshed. As the threshed straw forms a straw-chaff-grain mixture, the sieves are overstrained. To improve the capacity of the sieves, different systems are provided. It is known, to provide adjustable finned sieves. These sieves, however, have the disadvantage that a gap is formed between the single fins which are attached transversely to the air stream. Stems, which are lying transversely or parallel to the conveying direction, enter the gap and are passed to the lower sieve. This is due to the fact that the stems do not have enough surface area so that the air stream can blow the stems to the back. If the air stream is increased so that the stems are transported to the back, harvesting material is also blown beyond the sieve and the sieve box, which leads to a non-acceptable loss of harvesting material. The adjustability however has the advantage that the adjustment angle of the fins can be changed compared to the conveying direction and to the air stream. This becomes disadvantageous, when the driver of the combine-harvester is not in position to find the correct setting corresponding to the harvesting material. Instructions for the settings do in fact exist for the different grain types. However, the different harvesting conditions are so manifold, that a proposed setting can sometimes be completely wrong. Undergrowth, brittle straw, the moisture content of the straw, the grain and chaff parts play a role to provide wrong settings. Work on inclined areas or hilly areas is a decisive influence for wrong settings since these parameters can not be accounted for by any predetermined setting. Thus, the respective optimum settings adapted to the harvesting conditions are thus only found by very experienced drivers. To optimize cleaning of the harvested material, it is necessary to open the sieves as far as possible. However, this is not normally done since the grain flow rate is too small and the actual power capacity of the expensive combine-harvester is not used to full capacity.
Adjustable fin sieves have another disadvantage. Due to their design, their weight is high and the shaking drive of the sieve device is correspondingly strongly strained. This causes unwanted vibration, which can be transferred through the whole machine. Furthermore the suspension is effected by strong wear. Accordingly, the sieve is worn out after a few harvesting periods and has to be replaced. Further such fin sieves are complicated and expensive in their manufacture.
Utility model DE 76 32 151 U discloses an alternative sieve design. Here, a section of the sieve parallel to the conveying direction has a sieve surface with a zigzag arrangement. One leg of each portion is arranged with a smaller inclination angle than the other one to an imaginative horizontal plane. The leg, which is arranged in front in the conveying direction, is arranged with a smaller inclination. The leg arranged behind in the conveying direction has large through-holes, which are formed in the form of windows. The grains fall through the windows to reach the bottom downwards to the conveying device or to the following sieve. A disadvantage of this system is that straw stems, which are aligned in the conveying direction, reach into the openings directed downwards in an inclined manner and cannot be blown to the back by the blower wind. The stems move from the first sieve against the conveying direction down and are mixed with the harvesting material or the stems strain the fine sieve, which is arranged below the first sieve.
U.S. Pat. No. 5,176,574 discloses a sieve, which is similar in its basic design to the sieve according to the above mentioned utility model. Here, the single fins, which in the cross-section are angled, are arranged continuously transversely to the conveying direction. Each fin lies against the neighboring fin and is respectively connected to it. The advantage of such a sieve is the high grain flow rate capacity, its inexpensive design, as well as its light weight. Its non-adjustability means that no error-settings can be carried out. The disadvantage of this sieve is that straw stems, which are aligned in the conveying direction, can enter the passage openings inclined downwards and become wedged there or the stems strain the below arranged fine sieve.
It is an object of the present invention to provide a simple and light sieve in its basic design, which combines a high flow rate capacity with an optimum cleaning efficiency. The sieve is also usable for the majority of different harvesting materials.
The object is solved according to the invention by a sieve, including a sieve surface, which when viewed in section, is arranged parallel to the conveying direction. The sieve has a basic profile with a zigzag arrangement. The zigzag is constructed by repeated consecutive portions with each including a first leg and a second leg. Both legs are arranged such that they enclose an angle between each other. The first leg is arranged ahead of the second leg in the conveying direction. The first leg is arranged at an angle to a first imaginative horizontal plane. The angle is smaller than the angle, which the second leg encloses with said first plane. Both legs form a groove. The groove is arranged transversely to the conveying direction. Openings are arranged in the second leg in a distributed manner. The respective first legs are provided with an extension, which ends in an edge. The extension projects in the conveying direction beyond the connection area of the first leg with the second leg. Thus, the extension is arranged ahead of the second leg in the conveying direction. The extensions are arranged along the first leg in the transverse direction to the conveying direction.
In this embodiment it is advantageous that straw stems, which are aligned in the conveying direction, are held higher by the extensions above the leg with the openings through which the grains fall. Further they are transported by the edges in the conveying direction. Therefore, the stems are effectively prevented from entering into the openings, which receive the grains. Thus, the sieve ensures that the fine sieve arranged below the first sieve can be kept free of stems. Accordingly, the fine sieve is not clogged. A straw stem, which is transversely aligned to the conveying direction, is accelerated in the following oscillating amplitude by the solid part of the second leg which remains between the openings. Accordingly, the stems are further conveyed in the conveying direction. Furthermore stems, which are aligned transversely to the conveying direction, compared to the stems which are aligned parallel to the conveying direction, offer a relatively large attack area for the air stream. Thus, the stems with the support of the oscillating amplitude and the air stream are transported without problems in the conveying direction.
In an embodiment according to the invention, the extension is arranged nearly in a plane with the first leg. It is possible to attach the extension on or to the first leg. Various known welding methods can be used for the connection. An integral arrangement with the first leg is also sensible.
An improved effect is achieved by the edge of the extension reaching nearly up to a second imaginary plane. The second imaginary plane is arranged at a right angle on the first plane and the connection area between a first leg and second leg.
A simple way to manufacture the sieve surface is to construct it from profiles running transverse to the conveying direction. Each profile corresponds, respectively, to a portion. Each profile has a connection leg which projects, when seen in a section parallel to the conveying direction, from the end of the second leg to the first leg in an opposing direction. Also, the connecting leg is arranged parallel to the first leg. A type of Z-profile is achieved. The profiles are connected to each other, respectively, to form a sieve surface. The profiles can be made from metal sheet, especially by bending the steel sheet. It is also possible to make the profiles from casting of aluminum or plastic material, for example. It is also possible to design the whole sieve as a casting component from aluminum as well as plastic material. To further enhance the edge, the extension is formed as a zigzag. Instead of the zigzag arrangement, a sharp-edged arrangement can be chosen. Especially by a zigzag arrangement the stems are prevented from sliding onto one side of the sieve in a working location on a slope.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.